All Maggy's need a serious breakin before they sound right. 20 to 40 hours is necessary. The bass from Maggy's is different than what a box speaker produces. Even the larger ones may seem to be bass shy at first. They do have good bass but there is no mid bass hump. They make a bowed bass sound right.
They do like lots of current! The Rotel you have is more than sufficient. Just remember to give them breathing room in back. 2 to 3 feet from the wall is a good place to start with any panel speaker. The area behind them should be a mix of reflective dispersive and absorbant materials. if you must err do so on the reflective side. You don't want the rear radiation sucked up. That will kill soundstage depth. I used to own Maggy's but have since moved on to full range ESL's. I have been recommending them to people for the last 15 years. Six of my buddies have switched to Maggy's. One to 3.6R's, one to MG-3's, 2 to MG-1's and 2 went from all in one K-Mart specials to modest systems with MMG's. They are all quite happy. The 3.6 owner traded up from MG-2's.
The MMG's are the Maggy's that benefit the most from a decent subwoofer. The smaller diaphragm just can't move the amount of air larger ones can.
In any case, if you don't like them you can just return them.
If the Magneplanar sound is new to you, boy are you in for a surprise!